1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device and, more particularly, to a method for forming a trench type isolation film.
2. Description of the Related Art
As semiconductor devices become more highly integrated, the gap between individual semiconductor devices on a semiconductor substrate becomes narrower. Therefore, it becomes very important to electrically insulate the semiconductor devices from each other.
Various types of isolation films are used in the processes involved in manufacturing a semiconductor device. A local oxidation of silicon (LOCOS) type isolation film and a trench type isolation film are representative types.
The LOCOS type isolation film is widely used since it is easily formed, although it occupies a wide area in the semiconductor substrate. This is due, in part, to the formation of bird""s beaks which extend into active areas of the semiconductor device. However, as the distance between the semiconductor devices becomes smaller due to the increasing integration of the semiconductor device, the LOCOS type isolation film is replaced by the trench type isolation film which occupies a relatively narrower area on the semiconductor substrate.
Referring to FIG. 1, a trench type isolation film 14 according to a conventional technology is formed by forming a trench 12 in a semiconductor substrate 10, filling the trench 12 with an insulating film 14, and flattening the insulating film 14.
The conventional method for forming the trench type isolation film has the advantage that the geometry of the trench, i.e., the depth and the width of the trench, may be controlled to correspond to the high integration of the semiconductor device. Also, it is possible to increase isolation efficiency by selection of the insulating film used for filling the trench.
However, the process of forming a trench type isolation film is more complicated than for the LOCOS type isolation film because the substrate must be etched to form the trench. Also, the subsequent formation of a gate oxide film often results in contamination due to the insulating film filling the trench. This contamination often occurs at the surface between the semiconductor substrate, particularly that portion near or contacting the trench, and a pad oxide film. If the contamination is present when the gate oxide film is formed, the thickness of the contaminated portion of the gate oxide film 16 becomes thinner than the thickness of other portions, as shown in FIG. 2. As a result, the characteristic of-the gate oxide film deteriorates. For example, the break down voltage of the gate oxide film becomes lower. In addition, the contact leakage current of P+/N or N+/P increases due to the contamination and a shallow pit is formed in the field area.
It is a desired feature of one embodiment of the present invention to provide a method for forming a trench type isolation film by which it is possible to prevent the characteristic of a subsequent process, in particular, the characteristic of a gate oxide film from deteriorating by contaminants of a previous process.
Toward achieving the above feature, a method for forming the trench type isolation film according to an embodiment of the present invention proceeds as follows:
(a) An active area and a field area are set on the semiconductor substrate. (b) A mask layer, by which the field area is exposed, is formed on the semiconductor substrate. (c) A trench is formed in the field area using the mask layer as an etching mask. (d) An insulating film for filling the trench is formed on the substrate. (e) The substrate on which the insulating film is formed is first annealed. (f) The entire surface of the insulating film is flattened until an underlayer of the insulating film is exposed. (g) The flattened resultant is second annealed.
In the processes, the insulating films which are composite films are first and second oxide films. The first oxide film is an undoped silicate glass (USG) film. The second oxide film is an oxide film (a PE-TEOS film) formed by a plasma enhanced CVD (PECVD) method based on a tetra-ethyl-orthosilicate (TEOS). Also, the second oxide film is an oxide film (a PECVD oxide film based on SiH4) formed by the PECVD method based on silane SiH4 or an oxide film (an HDP film) using high density plasma.
According to another embodiment of the present invention, the first oxide film can be formed of the HDP film. At this time, the second oxide film is formed of a CVD film based on O3-TEOS.
The first oxide film is preferably formed to have a thickness which is the same as the depth of the trench.
The insulating film filled in the trench is flattened by a chemical mechanical polishing (CMP) or an etch back.
The trench is formed after forming a mask layer for exposing the field area on the semiconductor substrate, using the mask layer as an etching mask.
The mask layer is a pad oxide film and a pad nitride film which are sequentially formed.
The second annealing is performed by the following four methods.
First, the second annealing is performed in a state in which the mask layer is formed on the active area.
Second, the second annealing is performed after removing the nitride film of the mask layer.
Third, the second annealing is performed after removing the mask layer.
Fourth, the second annealing is performed after removing the mask layer and ion implanting conductive impurities into a necessary area of the resultant in which the mask layer is removed and before forming a gate oxide film.
The second annealing is preferably performed at a temperature no less than 1,000xc2x0 C. However, it is more preferable that the second annealing is performed for about an hour under a nitride atmosphere maintained at about 1,050xc2x0 C.
A method for forming the trench type isolation film, in which the trench is filled with the composite film, the filled material film is flattened, and the resultant is annealed before forming the gate oxide film, is provided.
According to the method for forming the trench type isolation film according to the present invention, it is possible to prevent the characteristic of the gate oxide film from deteriorating due to the contaminants generated during a process of filling the trench with the composite film. For example, it is possible to prevent the thickness of the gate oxide film from becoming thin, the leakage current of the P+/N or N+/P contact surface from increasing, and the shallow pit from being formed.
Briefly, according to another aspect of the present invention, there is provided a method for forming a trench type isolation film in a semiconductor device. The method includes forming a trench in a semiconductor substrate, filling the trench in the semiconductor substrate with an insulating film, annealing the semiconductor substrate and the filled trench, flattening an entire surface of the insulating film, and annealing the flattened resultant.
Briefly, according to another aspect of the present invention, there is provided a method for forming a trench type isolation film in a semiconductor device. The method includes setting an active area, setting a field area, forming a mask layer, forming a trench, filling the trench, first annealing, flattening, and second annealing. The active area and the field area are set in a semiconductor substrate. The mask layer is formed above the semiconductor substrate, and the mask layer is configured such that it does not cover the field area on the semiconductor substrate and such that it does cover the active area on the semiconductor substrate. The trench is formed in the field area of the semiconductor substrate, and the mask layer is used as an etching mask. The trench in the field area of the semiconductor substrate is filled with an insulating film. The semiconductor substrate and the filled trench are first annealed. A top surface of the insulating film is flattened until at least a portion of a layer below the insulating film is exposed. The flattened resultant is second annealed.